Sigma detection rules, expert-reviewed

Malicious Regsvr32 Executing DLL From Windows Temp

This rule detects regsvr32.exe registering or executing a DLL located in the Windows Temp directory which the ALPHV intrusion used after a VBS dropper wrote a payload there and this matters because regsvr32 loading a DLL from Temp is a common proxy execution and squiblydoo style evasion pattern that legitimate software does not exhibit.

Masquerading Exchange Server Impersonation via PrivExchange Relay Attack (via security)

This rule detects relays Exchange server authentication to abuse Exchange servers permissions and escalate privileges.

Malicious Remote Shell Execution via SMB Admin Share (via security)

This rule detects execute a remote shell via the admin share.

Suspicious DUser DLL Sideloading by credwiz via Image Load

This rule detects the Credential Wizard binary or its renamed variants loading DUser.dll from outside the System32 directory, the DLL side-loading technique Secret Blizzard used to launch its TwoDash and related backdoors. A signed host binary loading a same-named DLL from a non-system path is a hallmark of side-loading based execution.

Malicious WinGUP Updater Sideloading libcurl via gup.exe (via image_load)

This rule detects the WinGUP updater gup.exe loading a libcurl.dll from outside its normal install directories. The BoryptGrab-lineage infostealer distributed through fake GitHub repositories abused this signed updater to sideload its malicious loader DLL from user-writable paths.

Suspicious Masqueraded Windows Update Python Script Execution

This rule detects the Python interpreter executing a script masquerading as a Windows update named Windows Update Script.pyw, as dropped by the DeceptiveDevelopment ClickFix chain alongside drvUpdate.exe. The naming disguises attacker code as a benign system task, so catching the interpreter launching this file exposes the initial foothold.

Malicious Defender Exclusion Added via Add-MpPreference During Medusa Intrusion (via process_creation)

This rule detects PowerShell adding a Microsoft Defender path exclusion via Add-MpPreference, a defense-evasion step Storm-1175 uses to carve out an excluded location such as the C drive root before staging tools during Medusa ransomware operations. Adversaries blind Defender in this way to run payloads without detection, so an exclusion added from the command line ahead of impact is a high-confidence sign of an active intrusion.

Malicious Microsoft Defender Tamper via Registry Modification

This rule detects registry modifications that disable Microsoft Defender protections under the Windows Defender policy keys. Attackers set DisableAntiSpyware or DisableRealtimeMonitoring to switch off protection persistently, a registry-based evasion technique covered in Sekoia detection engineering.

Malicious WeaXor Ransomware Encryption Artifacts on Disk (via file_event)

This rule detects file system artifacts left by WeaXor ransomware, namely files renamed with the wex extension and the dropped RECOVERY INFO note. It indicates active encryption on the host.

Suspicious DotNet Utility Spawned by Script Host for Hollowing (via process_creation)

This rule detects RegAsm, MSBuild, or AddInProcess32 launched by a script host or mshta. This layered loader spawns these signed .NET utilities as process hollowing targets for its final payload.

Malicious Windows Defender Exclusion for Windows Dell Folder

This rule detects Add-MpPreference adding a Defender exclusion path for a Dell folder under the Windows directory, a Prometei defense-evasion step. The botnet staged modules such as its Mimikatz variant in C:\Windows\Dell and excluded that path from Defender scanning. A Defender exclusion for a non-standard folder inside the Windows directory strongly indicates malware hiding its working directory.

Malicious RDP Session Hijacking via tscon Command Line

This rule detects execution of the native tscon.exe binary with a destination session and an rdp-tcp or console source argument, the living-off-the-land technique used to hijack another user's Remote Desktop session without their credentials. Adversaries with SYSTEM privileges connect an existing session to their own to inherit the victim's access for lateral movement and privilege escalation. Interactive tscon usage targeting another session is rarely legitimate.

Malicious Curl Download From C2 CAPTCHA Path via Process Creation

This rule detects curl.exe retrieving a payload using the misspelled /capcha URL path pattern used by the KongTuke fake-CAPTCHA campaign documented by Cisco Talos. The tool is invoked by a PowerShell downloader to pull the next stage from hardcoded command-and-control infrastructure. Detecting it identifies active second-stage retrieval over an attacker-controlled channel.

Malicious Impacket SMBexec Service Registration - Native (via security)

This rule detects register the SMBexec service to estasblish persistence. Note that service registration is not always performed and that is recommended to use the related registry SYSMON rule to increase detection reliability.

Malicious OAuth Application Granted Full Mailbox and EWS Permissions (via m365)

This rule detects OAuth application permission grants for high privilege mailbox scopes such as full_access_as_app EWS.AccessAsUser.All and ApplicationImpersonation. Midnight Blizzard granted these permissions to attacker-controlled applications to access mailboxes across the tenant.